I just ate an entire medium pepperoni pizza for dinner and my roommate started lecturing me on how I'm gonna die in my 30s.
Does eating fatty and sugary foods make your life any shorter?
To answer your questions:
Sugar-sweetened beverage consumption is associated with a significantly elevated risk of type 2 diabetes, whereas the association between artificially sweetened beverages and type 2 diabetes was largely explained by health status, pre-enrollment weight change, dieting, and body mass index.
Rates of overweight and obesity have been on a steady rise for decades, and the problems society faces from this and associated metabolic diseases are many. As a result, the need to understand the contributing factors is great. A very compelling case can be made that excess sugar consumption has played a significant role. In addition, fructose, as a component of the vast majority of caloric sweeteners, is seen to be particularly insidious. Evidence shows that fructose bypasses many of the body's satiating signals, thus potentially promoting overconsumption of energy, weight gain, and the development on insulin resistance. It has also been shown to increase uric acid levels, which in turn promotes many of the abnormalities seen in the metabolic syndrome including hypertriglyceridemia. However, the main source of fructose in the diet is high-fructose corn syrup (HFCS), an artificially manufactured disaccharide that is only 55% fructose. This review highlights the fact that limited data are available about the metabolic effects of HFCS compared with other caloric sweeteners. The data suggest that HFCS yields similar metabolic responses to other caloric sweeteners such as sucrose.
—The Effect of High-Fructose Corn Syrup Consumption on Triglycerides and Uric Acid, by Theodore J. Angelopoulos, Joshua Lowndes, Linda Zukley, Kathleen J. Melanson, Von Nguyen, Anik Huffman, and James M. Rippe
Different type of fats have different effect, often, but not always, negative. These are the USDA 2010 "Dietary Guidelines for Americans":
Consume less than 10 percent of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fatty acids.
Consume less than 300 mg per day of dietary cholesterol.
Keep trans fatty acid consumption as low as possible, especially by limiting foods that contain synthetic sources of trans fats, such as partially hydrogenated oils, and by limiting other solid fats.
The document has a large section dedicated to the effects of fats and references.
A recent study of individuals of Ashkenazi Jewish descent aged 95 and older compared against a database of information of those who did not live as long showed evidence that genetics may play a more significant role in longevity than lifestyle choices such as diet, smoking and drinking alcohol.
According to a recent news article on the study:
The researchers concluded that these findings suggest genetics play a role in lifespan and found that there was no difference in lifestyle factors, including BMI (an indicator of obesity), smoking and alcohol consumption, between the [longer vs shorter lifespan] groups.
The researchers were quick to point out that this isn't a license to behave in an unhealthy manner and it might be argued that 'quality of life' issues become a much bigger factor than longevity at these advanced ages. For example, a high BMI indicating obesity also puts you at risk for type 2 diabetes, which if improperly managed can lead to amputations, loss of vision and have other significant quality of life impacts.
Arguably, the adoption of a more Western diet eliminated the higher than average life expectancy which the people of Okinawa enjoyed.
The prevalence of heart disease and cerebrovascular disease increased. The article summary describes the main dietary changes:
Also, as of 1988, daily intake of green and yellow vegetables in Okinawa was about 50% higher than the national average. However, by 1998, daily meat intake and fat energy ratio had surpassed 100 grams and 30%, respectively, and daily intake of pulses and green and yellow vegetables had declined to the level of the national average.